precision mediump float;


uniform vec2 u_resolution;
uniform vec2 u_mouse;
uniform float u_time;

void main() {
    vec2 st = gl_FragCoord.xy / u_resolution;
    st.x *= u_resolution.x / u_resolution.y;
    // gl_FragColor = vec4(st.x,0.,0., 1.);
    // gl_FragColor = vec4(0.,1. - st.y,0., 1.);

    st = (st - 0.5) * 2.;
    float d = length(st);
    // gl_FragColor = vec4(vec3(d),1.);
    gl_FragColor = vec4(vec3(d),1.);
}